Making Pigments :: Paintings :: Grosse is a geek

Making Pigments
Sometimes, you need to have something that you can't get anywhere.

Obtaining pigments is usually fairly easy but some are a little more difficult to get hold of than others. Here are three pigments that I have made for different reasons:

Dutch Stack Lead White

Verdigris

Malachite

I made:

Dutch Stack process Lead White simply because:

it is difficult to obtain;

it is expensive - it really needs to be a reasonable price compared to how much effort needs to be made to get just what you want and I object to paying as much as £1 per gramme for it (although some places sell it for around 10p per gramme) when you can make it for around £3.50 - £4.50 per kilo;

you don't know if it is adulterated - zinc white or titanium white is added to a lot of white pigments;

you don't know if it is stack lead white - it might just be precipitated lead carbonate or just precipitated lead hydroxide;

you don't know if any of it is actually lead - sometimes you get a 'safe' version of a pigment;

real lead white paint is 'stringy' - let it drip from a brush and it forms strings - whereas commercial lead white is 'buttery' just like every other commercial colour; and,

It is synthesising a pigment using a traditional method in a pigment where it does make a difference

Verdigris because:

it is difficult to obtain;

it is expensive - at around 50p per gramme to buy when you can make it yourself for around 5p per gramme

you know what is in it if you make it yourself

It is synthesising a pigment using a modern method in a pigment where it doesn't make a difference

Malachite because:

it is difficult to obtain;

it is expensive - at around £1.50 per gramme to buy when you can make it yourself for around 12p per gramme

you know what is in it if you make it yourself

It is making a pigment from the original rock using a traditional method in a pigment where it does make a difference

I made them for water and oil colours.

Before we get started...

SAFETY FIRST.

Many pigments are toxic to some degree - either in low doses over a long time or in higher doses in a single instance (cronic and acute poisoning respectively) - so, it is important for your own safety and that of those around you to adopt certain practices that will preclude such events.

To contaminate yourself with pigments (or other painting-related compounds), there are a number of routes into your body. The most obvious of these is your mouth. Others include your lungs, skin, nose, eyes and so on. Avoiding activities that allow things to come into contact with these routes is the most effective way of avoiding contamination. So, when painting or preparing pigments, paint, solvent:

Do not smoke. Apart from the obvious fire hazard with organic solvents, you will be putting things in your mouth that you have handled with your fingers;

Do not eat or drink for the same reasons;

Keep your painting related activities in an area that is away from your normal living area (you will be less vigilant when not painting so more likely to become contaminated);

Keep away from pets, partners and children, whether the materials are in current use or not;

Pigments are powders that you can breathe in so keep the dust level down by prevention - when mixing pigments, do things slowly and using as little force as possible thereby reducing the energy that can throw powder into the air.

Do not paint when intoxicated - you will not be as aware of the potential dangers;

Wear protective clothing so that your everyday clothes do not become contaminated - an apron will do, just something that is going to stop whatever it is that you are working with coming into contact with you or your clothes;

If you become aware that you might be breathing in more solvent than is healthy, increase the level of ventilation (if you are gilding, don't do it where there are solvents anyway as you cannot have drafts with such an activity.

Finally, clean up after you have finished. You don't want pigments mixing together but more importantly, you don't want to pick up any contamination from stuff that has not been cleaned away which you can then ingest by accident.

The above is not an exhaistive list. Feel free to be even safer in areas that are not mentioned above as well as those that are.

Dutch Lead White

What is lead white? Lead white can be found in nature as the mineral 'hydrocerussite' but it has been made artificially for so long that the man-made version is found just about everywhere since lead has been smelted. Apart from hydrocerussite, Lead white is the white compound that you get from weathered lead pipes/roofing. It is what happens when lead metal has a chance to react with the environment over a long period of time. Pipes and roofs are quite resistant to corrosion so thousands of years ago, someone found a way of speeding it up.

First of all, this is what lead white is...

2 Pb CO₃-Pb (OH)₂

for the non-chemist, hover the mouse over
the parts of the formula to see what they are.

You can see from the formula that it is a lead compound of atmospheric water and carbon dioxide.

The formula weight of this is 755.6g/mol with three lead atoms at 208g/mol so 100g of lead metal will make roughly 121g of white lead pigment.

The reaction goes like this:

exposed metalic lead is attacked by acetic acid vapour in the presence of oxygen and water vapour (the latter allowing the acetic acid to be an acid as opposed to just an organic solvent) and forms lead acetate;

carbon dioxide in the air displaces the acetic acid to make lead carbonate

water in the air replaces acetic acid to make lead hydroxide

the acetic acid goes on to attack the metalic lead further

This reaction will happen without the acetic acid there - commercial lead sheet for roofing has a protective compound on the surface to help prevent this from happening - but it will happen painfully slowly. The acetic acid acts as a catalyst - changing the rate of reaction - in this case speeding it up enormously so instead of taking 100 years to eat a hole in the sheet, it will all have rotted through in somewhere between 6 months and a year, depending upon your climate.

So, what do we need and where can we find it?

Lead sheet - the reaction happens on the surface so the larger the surface area to mass ratio, the more we produce for the lead we buy in a given time;

Acetone - this is to remove the labelling from the lead sheet and also any protective layer from the surface of the lead;

Acetic acid - as said above, this is the catalyst for the reaction. You can buy glacial acetic acid online fairly easily. It is called 'glacial' because pure acetic acid freezes at 16.6C which is only a few degrees below room temperature and during winter, it will freeze solid. Glacial acetic acid is 100% acid and although it is the same acid that is in vinegar, that is only 5% so sprinkling glacial acetic acid on your chips (fries in the US) is both dangerous and an act of sheer stupidity;

Containers that are rugged, watertight and corrosion resistant

plastic spacers - you can make these out of old pop bottles; and,

If you are in the UK and the same happens to you as it did to me, you will also need:

a length of silicone tubing (5-10m depending upon circumstances);

an old 2 litre pop bottle;

ordinary granulated sugar;

yeast;

Later on, you will need:

solid sodium hydroxide;

solid sodium carbonate;

a dedicated mortar and pestle;

filter papers;

a funnel; and

plastic jars.

as well as rubber gloves, goggles apron or lab coat and so on.

So, we can buy lead and acetic acid that are pure enough, water comes out of the taps and there is oxygen and carbon dioxide in the air. Whilst the oxygen level is a nice 21%, the CO₂ level is only around 400ppm which is far to low so we need to increase that quite substantially - we need a carbon dioxide generator.

'Really Useful Boxes' produce boxes that are rugged and made of the right materials for this project so I got a large one and four smaller ones that would fit inside. The idea was that I would put a carbon dioxide generator in one of them, leaving the others to put lead spirals in.

You can get lead that is suited really well to a project like this in the form of 'Code 3' lead strip which I got online as a 3m roll at 150mm wide (7kg of lead ~ £850-£8,000 worth of lead white depending upon whom you buy it from). Code 3 is 1.32mm thick which translates to 14.97kg/m². Here, I'm making it only for my own use, I am not selling it on (or even giving it away) so I don't need to make that much of it in one go. I can use the plant to make a kilo or so then put it somewhere safe until around 18 months before I need some more.

To prepare it, I removed the sticky label with a knife then some acetone to remove the remaining glue. Then, I scrubbed the surface to remove dirt, lead oxide and anything that might be there to protect the surface then I swabbed it with acetone again to remove anything that I couldn't see - this stuff is supposed to last 100 years but I needed it to go a bit quicker than that.

I cut around 350mm off the roll and cut it down the middle, lengthways to get two strips at 75mm wide totalling around 800g so that I would end up with just under a kilo of white lead pigment.

Next, I rolled them into spirals and placed them on plastic spacers that I had made by zigzag-folding some plastic pop bottle side cut to around 1cm wide strip so that they were a centimetre or so off the floor of the plastic container. The lead coils don't have to be coils, you can have them as zigzags - the only requirement really is that the air can get to them.

In the diagram, the lids of the lower cells have been rested on the tops of those cells sideways so that the atmosphere inside the larger container can move around freely to avoid a situation where each cell has its own micro atmosphere.

Next, I added around 5mls of glacial acetic acid to the bottom of each of the cells that I was using, along with some water.

Now, it was time to generate some CO₂.

I started off with some sodium carbonate (not bicarbonate - carbonate has twice as much carbon dioxide in it per molecule than sodium bicarbonate) to which I added some water to dissolve it and some hydrochloric acid from a toilet cleaning product in one of the cells as per diagram 'A'. It all fizzed nicely so I put it in the office and left it but not a lot seemed to be happening so I checked for the CO₂ level using a lighted taper and there was none. Failure.

Next, I emptied out the cell that I had used for the generator and three-quarters filled it with warm water into which I had dissolved some sugar and then added some yeast. The top of the large container wasn't air tight so oxygen could get in still.

After a couple of days, there were complaints of the smell of acetic acid from it so it had to go outside. Outside, the British climate wasn't warm enough to let the yeast react so that had to be rethought.

So, I got an empty 2 litre pop bottle and two-thirds filled it with warm water into which I had dissolved some sugar and then added some yeast. I had some silicone tubing which I had put through a hole in the bottle's lid, ran down the outside of the building and into the lead plant. The bottle was in the warm and able to generate as much carbon dioxide as I needed. Every 5-10 days, I would change the yeast suspension for fresh and it would keep on going.You can see from diagram 'B' that now, we have enough room for four flake-producing cells.

Renewing the acetic acid and water to replace evaporation and consumption, I kept this up for well over a year.

This is traditional Dutch stack lead flake forming on one of the lead rolls. You can see why it is call flake white. If left, it will grow to between 5mm and 15mm thick but the thicker it is, the less oxygen, acetic acid and moisture can get through to the metal.

One thing that I noticed was that it took a while for the corrosion reaction to get going but once it had taken hold, it just went and went. Once I had finished this, I still had some unreacted lead coil left so I just laid it across the top of two of the cells - without any CO₂ generator or any extra acid and left it. When I looked at it next, a few months later, it had rotted through and collapsed where i had left it. So, if you are having a go at this and it is taking a while to get started, don't worry too much about it.

One thing that lead flake likes to do is to fall off the lead coil, into the acetic acid. When this happens, the acetic acid, which is a stronger acid than the carbonic acid that creates the carbonate, is displaced to make lead acetate which is readily soluble in water. As the water and acetic acid evaporate off, they leave behind the lead acetate which gets so concentrated that lead acetate crystals start to grow and these can end up quite long - I found one that was at least 7cm long.

So as to prevent this, just harvest the lead at regular intervals - every 2-4 months - by carefully taking the coils out and bending them slightly so that the flake falls off into a container to be stored. Put the lead coil back and add some more acetic acid and water - leave the lead acetate in there - it isn't going anywhere.

Once you have enough lead flake that you feel that you can process it, harvest the lead flake and put it with the rest that you have collected and put the lead coils, what is left of them, to one side.

Lead Acetate

Now, you have a container that has lead acetate in the bottom so add some water to the crystals so as to dissolve them. We are not going to throw this away as it can represent quite a bit of lead and also, it is dangerous to the environment to have us making lead compounds and then not incorporating them into works of art.

The intention here is that you remove the acetate and replace it with the same anions that are in lead white - carbonate and hydroxide - but there is something else that you can do instead, although I would recommend that you keep the resultant pigment well separated from the lead white if you decide to follow that route.

Lead Chromate - chrome yellow - an interesting diversion.

If, instead of replacing the acetate with hydroxide and carbonate, you replace it with chromate, you will get lead chromate (PbCrO₄) which is a vivid yellow pigment, the preparation of which was published in 1809.

All you need to do is make a solution of potassium chromate and add that to the dissolved lead acetate then filter it off and wash it, eventually drying it then prepare your paint the same way that you would with any other pigment.

Modern Lead white

Make up some sodium hydroxide solution - be very careful not to get any solid or liquid anywhere. The small beads of this stuff can roll all over the place then react with the moisture in the air to make caustic soda solution which you can then end up getting on you. A small amount of this, even fairly dilute, can cause burns that can blind you or take literally months to heal. I would strongly recommend that the location that you choose to do anything at all with caustic soda pellets/beads is somewhere that can be washed down easily, like the bottom of a sink with a flat bottom, for instance. if you get any on your skin, it will feel soapy so rinse it off straight away with copious water, rubbing the solution as the water runs over it until it doesn't feel soapy any more.

Additionally and in a different container, make up some sodium carbonate solution - this isn't quite as dangerous as the NaOH solution but you still need to make sure that you remove any of it that you might get on you.

It doesn't matter that much how much of each you make as long as there is enough to react - as a rule of thumb, a nice excess (possibly around 2:1 or so) is taking the same volume of sodium hydroxide and of sodium carbonate as there is lead acetate.

Once they are all dissolved and well mixed, add roughly half of the lead acetate solution to the sodium carbonate solution and to the remaining half of lead acetate solution, add the sodium hydroxide solution. It doesn't matter which sodium solution you use first, it is just that by pouring the last one into the lead acetate solution, you are not adding lead to another container.

When you do this, a fine precipitate of lead carbonate and in the other container, lead hydroxide will form, taking out any lead in there. Next, add some water to each, mix them around and then let them settle. Once they have settled, carefully pour off the excess water and sodium salt solution and then add more water and repeat the washing, settling, pouring routine. Next, add some water and mix the two precipitates. You now have a modern synthetic lead carbonate/ hydroxide that isn't flake white although chemically, it is similar. You can decide whether or not you want to add it to the actual flake white that you have made or keep it separate and process it parallel to the actual flake white.

Traditional Lead white

This is what you need to do now that you have your flake white (and to the lead white that you have recovered from lead acetate or chrome yellow that you have made from the lead acetate).

Put your flake white in a container and break up the flake, removing any bits of lead metal as you go and putting them to one side. You can put them back in your container and let the flake reaction continue.

Next, a bit at a time, put some lead flake into the mortar and add some water. Grind it until you think it is fine enough and then tip this into a container. Repeat the process until you have processed all of the lead. Then, add a bit more water and leave it to settle.

Once it has settled, you might notice that the water has a slight blue tinge to it. This is because in the lead process, some copper ends up in the lead roofing as an impurity. As this is water soluble, it is not a problem as it will be removed when you tip the water away. Lead white isn't very soluble in water so you aren't going to lose any appreciable quantity in this process if you have let the water clear properly.

So, tip away that water - it doesn't matter if there is a bit left behind, add some more water, give it a good stir around and let it settle again. Do this several times until you feel happy that you have removed any impurities.

Next, add some water to make a slurry of your now clean lead white. Get a filter paper and filter some of the slurry until you have possibly 10 cubic centimetres of solid flake. Take that filter paper and fold over the top then put it on some kitchen towel. Keep on doing this until you have done all of the flake white.

Fold over the paper towel and gently squeeze the water out of it, replacing paper towels as necessary, until they feel fairly stiff. Then, again, on kitchen towel, but on a flat portable surface such as a tray (you might want to put some clingfilm over the surface of the tray first), arrange the little chunks of lead white, still in their filter papers on the towel and then, over the coarse of a few weeks, let them dry out.

Finally, peel away the filter paper and put them in a plastic jar, weigh it, label it and store it in a dry place away from children and animals - a safe of some sort is probably a good idea for solving ths problem.

Some people leave the lead white to mature - this can really only represent and opportunity for any remaining lead that didn't get taken out to oxidise so that you don't end up with lead metal in your paint.

Verdigris

What is Verdigris? analogous to lead white, verdigris is the product of atmospheric action on copper. Malachite is what happens to copper when you leave it out in the rain, like lead white is to lead. However, verdigris is more complex than that depending upon its circumstances of production and your point of view.

'Natural' verdigris can have in it copper carbonate, hydroxide, chloride, acetate and anything else that happens to be knocking around in the environment. It is the turquoise salt that you see on copper pipe fittings in the gents and in older houses because, like its lead analogue, it takes a long time to form.

'Synthetic' verdigris has been around as long as Dutch Stack Lead White and is made in the same way where copper sheet is suspended above acetic acid and allowed to rot through, producing the turquoise crystals or powder. However, this does not build up in layers in the same way that lead white does and you can make it by other methods and it is the same product both chemically and physically - in other words, unlike Dutch Stack Lead White, there is no advantage to doing it the slow way - any process will do and the result will be the same. The formula is this...

Cu(OOCCH₃)₂H₂O

So, as you can see, there is one water molecule of crystallisation for each copper atom. You can make this by having a source of copper salt and displacing the anion with acetate from acetic acid.

One variant - just to add to the complication - is a version with a molar amount of copper hydroxide that is three times that of the copper acetate like so...

Cu(CH₃COO)₂.[Cu(OH)₂]₃.2H₂O

and you could make this by making your copper acetate then adding a measured quantity of sodium hydroxide to it to take out some of the acetate (sodium acetate is very soluble in water) to give you your mixture. In fact, you could add anything you like - acetic acid is a weak acid and will be displaced by any stronger acid so you can have some fun.

How Available is Verdigris? You can get verdigris from some places but it will cost you and - as you can see from the variants you can make yourself, you can't be certain of what you will get. You can buy the ready made stuff for £5 for 10g but you can make it for yourself for a tenth of that.

What About Making Your Own? You can make your own from copper sheet and acetic acid but that takes a long time and the results will not be any better than if you just synthesise it from other materials. Oxidising the copper without forming copper oxide is a potential problem so finding a source of copper salt that we can trust is the main issue but there is an excellent solution to it: Malachite is used a copper ore and a finely divided malachite powder is what is used by the pyrotechnic industry to get a green flame. The green flame is the emission spectrum of copper and if it is contaminate with something else, it will produce a different colour. So, if you look around the internet for 'malachite powder', you will find some at a good price. The other ingredient is acetic acid which you can pick up as glacial acetic acid - see Dutch Lead White above.

The Reaction is as follows...

4CH₃COOH + CuCO₃.Cu(OH)₂ => 2[Cu(OOCCH₃)₂H₂O] + H₂O + CO₂

Molecular weights say: 240g acetic acid + 221g malachite => 399g copper acetate + 18g water + 44g of carbon dioxide

So, if we want to make 100g of verdigris, we need: around 60g of glacial acetic acid and 55g of malachite and in the process, we can expect it to give off 6.6litres of CO₂.

So, what do we do?

weigh out the malachite powder and put it in a container that should be fairly big because of the amount of gas that is going to be given off.

Next, weigh in the glacial acetic acid and pour that into the container with the malachite in it. Nothing should happen. The reason for this is that the acetic acid hasn't got any water to grab to make acid - as far as the malachite is concerned, it is just an organic liquid that it doesn't dissolve in. Stir it around so that the malachite and the acid are mixed well.

Then, add literally a few drops of water. You should see some foaming going on as the water activates the acid and that then drives off the CO₂ so stir it around to make it complete the reaction and then, it should stop. Add a little more water, and do the same again.

As you add more and more water, two things should happen: the mixture gets hot as the reaction progresses; and, the foam goes further up the sides of the container each time.

The reason we have foam is that the acetic acid is like a short-chained detergent. It has an end that likes water and an end that dislikes water (hydrophylic and hydrophobic respectively). These line themselves up, side by side, to form membranes, one from of which is the bubble. As it takes acetic acid to do this, they are going to occur more as the concentration of acid increases so the more water you add, the more it foams. You can break down the bubbles and only add small quantities of water to get around this problem.

One thing you shouldn't do is add too much water. Copper acetate is soluble in water so the more water you add, the more pigment you lose.

Finally, you will stop getting bubble formation when you add water and you should now have a mass of turquoise powder in your container.

As with the lead, filter this off but there is no need to wash it and re-filter - any impurities that you don't manage to lose through the filter such as water and acetic acid are volatile and you will lose them in the drying process.

Next, spread it out and leave it somewhere to dry. If you want to speed it up, you can put it in a fan oven at no more than around 60C otherwise you are starting to get close to the temperature that it decomposes at.

Use the spatula to chop it up and turn it over as it dries and you will end up with a nice, crystaline powder like that on the right which was photographed whilst it was still a little damp.

Once you have a dry powder, bottle it up label it and store it in a dry place away from children and animals.

The final product will have a very slight odour of acetic acid but it s volatile and if you use this pigment in watercolour, that will disappear quickly.

Finally, whilst verdigris has a beautiful turquoise colour that remains in watercolour, something really quite odd happens when you use the pigment in oils.

If you make up some verdigris paint and paint a sample, over a period of a few days, it will become more green as it dries. Jan van Eyck used this pigment and it is stable - evidenced by the fact that the verdigris that he used still is green - it is just that before it becomes stable, it changes hue.

You can see this hue change in the sample I did on the right. The numbers for hue are those that you would get in an image processor going from 0° to 359° so you can see numerically that the change is significant.

Malachite

What is Malachite? analogous to lead white, malachite is what happens to copper when you leave it out in the rain, like lead white is to lead. Naturally occurring malachite forms in underground water systems when copper carbonate is precipitated only instead of forming crystals, it usually forms concentric spherical forms or botryoidal forms - it also has other forms but this is the one that you will be most familiar with.

How Available is Malachite? You can get Malachite from some places but it will cost you and - as you can see from the variants you can make yourself, you can't be certain of what you will get. You can buy the ready made stuff for £15 for 10g but you can make it for yourself for less than a tenth of that.

So, what do we do? First of all, Equipment and materials we need:

some malachite rock - the darker the better;

a mortar and pestle made from an appropriate material - Malachite has a hardness of 3.5-4.0 and Granite has a hardness of 7 so that will do fine.

a tea strainer or similar metal sieve - to define an upper limit on particle size;

a rubberised mat - this is mainly about noise abatement;

an appropriate plastic or glass container - this is to store the powdered pigment in after you have made it.

This is a 500g bag of firework-grade malachite powder so it has no other metal contaminants of any significant degree, along with a piece of malachite rock. You can see that the colour is a lot lighter in the powder which is what happens with malachite when it is overground - the same as with smalt, lapis lazuli, azurite and so on. Also, the hue of the powder is bluer than of the solid mineral - a particle-size-related hue change is what happens with cinnabar as well although the colour of the powdered cinnabar is yellower than the solid mineral.

This is a piece of malachite that I obtained from the Internet. It is around 5cm x 5cm x 1cm on average and weighs about 96g. It has been polished, presumably in a ball mill, but you can still see the saw marks on it where it has been cut from a larger rock.

Here, you can see the way that it grows in the wild. From the surface, you can see that the darker regions have larger crystals in them and as a result are more transparent that the lighter zones.

And here is a broken surface. You can see how the mineral has grown away from the surface of the underlying rock by looking at the bands as it has formed.

The mortar and pestle used here is a granite one that has an opening diameter of around three inches (about 75mm). I put the malachite pebble in it and basically hit it until it broke. Each bit that fell off got broken again and again.

One thing that I wanted to avoid was making the powder too fine so every now and then, poured the contents of the mortar into the sieve and shook it through so that the smaller material would not be ground further, returning the larger pieces to the mortar for reworking a small quantity at a time.

Eventually, after between half and hour and an hour, all of the rock had gone through the sieve and I re-weighed it.

I then weighed the powdered pigment that I had made and it came to 95g representing a loss so far in the process of about 1g and this can be accounted for as powder that got stuck in the interstices of the mortar and pestle.

To clean the mortar and pestle out, I first of all washed as much off it as I could with water and then I let it soak in acetic acid (around 50%) for about 10 minutes and that turned it into soluble copper acetate which I just then washed off.

One thing that you might notice is that it is not as saturated a colour as you might expect. This is possibly due to the fact that it is just coarsely ground rock at the moment and we haven't made any attempt to take that out and if you try making a water colour paint out of it, you get a horrid buff coloured scum on the surface of it which is just ground up rock..

If you tip the pigment into water and swirl it around then let it settle, you get this. You can see that there is a layer of different solid that has settled on top of the malachite - something that is easier to see if you look at it through a red filter (here, I have just used the red layer in the image).

One interesting point here is that the boundary between the malachite layer and the buff coloured layer is that the transition between them is quite narrow - this indicates that the settling rates are quite different so it will be easier to get rid of the top layer.

If you swirl the water around a bit, the lighter layer will get picked up a lot easier than the malachite as you can see from the whisps of fine particles - this is what we need to get rid of.

If you swirl it around so that all of the sediment is carried up by the water and the leave it for half a minute or so to settle, the malachite settles down first, leaving the dirty water on top.

You can wait for it to settle a bit more and then carefully tip off the dirty water or you can use a small plastic syringe (such as those that you get with inkjet printer ink refills) to suck the top layer off.

Just keep on repeating the process until the water left at the top is clean and if you let it settle right down the top of the sediment is malachite.

Once the pigment is pure enough for you, you can set out some filter papers on a non-absorbent surface and, using a spatula, spoon it out into little piles and spread it out so that the water can soak into the filter paper.

Use a wash bottle to clean everything into another container (this is one from an electric iron but you can use another flask or a beaker) then put a fluted filter paper into a funnel and then that into the Erlenmeyer flask.

Then, tip the malachite from the container into the fluted filter paper and let it drain.

This is the wet pigment on one of the filter papers. You can see it has a lot more colour but remember that it is wet.

Once the water has finished going through the filter paper, lay it out with the rest onto a tray of some sort that you have put a layer of baking paper on - the baking paper acting as a final catch-all in case of pigment falling off any of the filter papers.

Put them in a oven - not a fan over that is turned on as that will blow it all over the pace as it dries out - and leave them for half an hour to dry out.

Finally, weigh the container you are going to keep the malachite in and then put the now dry pigment in there.

I finally got 85g from my 96g of rock. Losses included the amount of bedrock that were included in the original rock.

I could make it more efficient by chiselling out any bedrock using a tungsten carbide point that I have as the botryoidal malachite itself has very little impurities within it.

So, I have 85g of malachite pigment for around £12 or £1.41 for 10g instead of £14.90 or $10.50 for 10g depending upon your supplier of choice.

Just in case you were wondering what the half-pan looked like if we didn't wash the pigment, it looks like this when you add water to it to paint with it.

Whilst it has been drying, the lighter rock 'scum' has worked its way to the top so when you add a few drops of water to it so that you can use it, you end up with 'scum paint'.

However, this can be to our advantage - if we add some water to the dried out block in the half-pan and let just the top dissolve, we can then wash this away with a short flood of water which reveals the largely scum-free paint block below.

This is what the half-pan of our purified malachite pigment looks like before it has dried. It still generates a little bit of scum but you can either use the same method as above to make it good or you can use a piece of kitchen towel to take it off the top before it dries.

So, we have gone through the process of floating off the impurities in the malachite by using the different rates of fall of the particles of malachite and the rocky impurities. Here, you can see test areas of paint - just water colours - to illustrate the problem and different ways of solving it.

Machine ground - this is the firework grade pigment you get. It is as fine as possible because you want the maximum surface area to mass ratio so the particles are very fine.

Without any separation, the brown rock impurity powder sits on top of the paint and gives it this awful, irregular, stained appearance.

Here, I have added water to the solid half-pan of paint that produced the previous sample (1) and let it soak into the surface very slightly, then I have washed it off with excess water. The brown scummy layer sits on top of the medium so as it sets, it accumulates at the surface of the solid cake of paint. You can see that washing off this layer of scummy paint has got rid of almost all of it as the hue has moved around quite significantly towards that of the machine ground pigment paint.

This area is of our separated pigment that has been ground into paint and it is quite a nice colour. It is substantially more saturated than the previous method (2) but you decide on which you want to do.

So, the malachite itself has impurities in it that will make your paint look brown and blotchy but this can be overcome by separation either before grinding in medium or after.

This set of colours is about particle size. You can tell from the photographs you have already see of malachite that the finer you grind it, the paler it gets. Here, I took the dry pigment and put it through the sieve quickly so that the coarser grains of pigment would be left. I then ground them in some medium, painting an area that you can see on the right as the process went on. The viscosity of the medium was a limiting factor as when the particles became really fine, it protected them from getting ground any finer. I ended up watering down the medium a bit to get the finest sample.

Machine ground pigment - I couldn't get anywhere near to this as the viscosity of the medium protected the pigment.

This is barey ground and is there for illustrative purposes only. You can see that the pigment is large chunks with a bit of powder colouring it but it does have a very nice green colour.

This one still has bits in it and is still on the coarse side for painting but it is getting there.

This is fine as far as hue and saturation go but it is still on the coarse side for painting.

This is good for painting but you can see that the saturation is starting to go.

This was as fine as I could get and you can see that it is starting to look a bit grey when compared to the two above it although it is nothing like as fine as the next sample - the machine ground standard (0).

So, you do need to grind it but you can see that there is an optimum particle size before the satuarion starts to drop off.

All images and original artwork Copyright ©2017 Paul Alan Grosse.